FRI289 It Takes A Village: Musashi And Its Associated Proteins In The Adenohypophysis

Disclosure: K.L. Bronson: None. L. Hardy: None. A. Lagasse: None. A.M. MacNicol: None. Musashi is an RNA-binding protein that regulates stem and progenitor cell fates. Interestingly, we have reported expression of Musashi pituitary stem cells as expected but also in the differentiated anterior pituitary hormone-producing cell lineages as well as. The adult anterior pituitary relies on the functional cellular plasticity of its hormone-producing cell populations to maintain endocrine homeostasis when physiological demands change. Both Musashi isoforms (Musashi1 and Musashi2) are highly conserved across species and have two N-terminal RNA-recognition motifs (RRMs) and a disordered C-terminus containing two regulatory phosphorylation sites. Musashi can selectively activate or repress the translation of mRNAs depending on the transcript and cellular context. While Musashi phosphorylation is required for translational activation, Musashi does not possess inherent enzymatic activity; therefore, co-associated proteins must mediate Musashi-directed translational control. Musashi immunoprecipitation studies initially identified 50 co-associated proteins in Xenopus oocytes, but only a subset of these were directly implicated in Musashi-dependent translational activation (e.g. Elavl1 and Pabp4). The identity of Musashi-associated proteins in the anterior pituitary and their requirement for Musashi function are not known. To this end, we have immunoprecipitated Musashi from whole male mouse pituitaries for mass spectrometry analysis. 206 proteins significantly (adj p-value < 0.05) associated with Musashi1 and Musashi2, and seven of these overlapped with the Xenopus dataset: Elavl1, Pabp4, Hnrnpc, Mov10, Pura, Rps27, and Upf1. Three proteins from the mouse mass spectrometry dataset were selected for further analyses. Sam68 is a multi-functional protein that sensitizes ovaries to FSH and LH, as well as mediates the activation of leptin and insulin signaling in a variety of tissues. Ago2 is a component of the RNA-induced silencing complex that is necessary for miRNA-directed translational control and is known to associate with Musashi1. The AU-rich element binding protein Elavl1 (HuR) contributes to Musashi-dependent activation of target mRNAs in Xenopus and also stabilizes Gnrhr mRNA in LβT2 cells and sensitizes them to GnRH signaling. We will present our ongoing studies on the requirement for these protein interactions for Musashi-directed mRNA translational regulation. Presentation: Friday, June 16, 2023